The present invention relates to the field of novelty filters.
Novelty filters highlight the moving or changed part of an image while suppressing the static part. One possible application can be anticipated in telecommunication systems. When transmitting images in telephone lines on a pixel by pixel basis, it is impossible to transfer all the information in real time without loss in the resolution due to limitations in the bandwidth. One solution to this problem divides the information into two parts, the static part of the information, which is sent once, and the changed part, which is sent in real time. An implementation of this process is to place an optical novelty filter operating at TV rates between the image and the transmission device to identify the changed part in the new frame.
Recently many novelty filters have been demonstrated. Some of them use phase conjugate interferometers while others utilize the nonlinearities which are inherent in two beam coupling. Some of them use phase conjugate interferometers while others use the nonlinearities which are inherent in two-beam coupling. Up until now all self-aligning novelty filters required high gain photorefractive crystals such as barium titanate or semiconductors or sillenites with high applied electric fields. Novelty filters using the more easily grown low gain crystals without electrical fields such as bismith silicon oxide (BSO) and GaAs have required careful and stable alignment of the external pump beams. See J. Khoury et al., Optics Comm. 71, (1989) 137.